Mount Elgon is an extinct
shield volcano situated on the border between Kenya and Uganda. It is the oldest
and largest solitary volcano in East Africa, covering an area of around
3500 km². The nepheline tuff-beds on the lower slopes of the mountain are
fossil-bearing and yield distinctive fossil wood (fig. 1-4). These layers of
volcanic agglomerate out-crop in caves on outliers of the mountain, such as
Walasi Peak on its western side. The petrified wood is particularly interesting
material as it marks the onset of renewed activity after a quiet period in the
volcanic history of Mount Elgon. Natrolite, calcite and naturalist minerals (fig.
5-6) have replaced the wood tissue. The mineralized wood fragments are all that
is left of the ancient forests that clothed the dormant volcano. Their age is
indeterminate; but the fossils are at least pre-Pleistocene in origin. The
topography and geology of Mount Elgon, and the petrography of its lavas, have
been described by Odman (1930) and more background on the fossil wood from this
locality can be found in a series of papers by Bancroft (1932-1935). Nowadays,
the area is protected by two National Parks (one on each side of the
Uganda-Kenyan border).